/sci/ - Science & Math

I did some math and I found an idea for a posts-Apollo SSTO derived from the Saturn V S-II stage:

S-II’s dry mass without engines is 27.3 tons.
The vehicle uses 3 Space Shuttle main engines (3.2 tons each). Let’s also say we use the Space Shuttle SRB parachute system - 3.9 tons.
Our vehicle uses three Falcon 9 style landing legs - 0.6 tons each.
Lastly, the heatshield. The shuttle’s heatshield had an area of 1,100 meters squared and a mass of 8.4 tons total. The 10 meter wide cylinder of the S-II SSTO has a base area of 75 meters squared, so even rounding up to 100 meters, it means our heatshield is a tenth of the shuttle’s. But we can round it up to 1 ton.

Putting it all together, we have a vehicle with a dry mass of 43.7 tons. We can round it up to 45 tons because of mass growth. The S-II stage held 443 tons of propellant, so there is a gross mass of 498 tons here.
The three SSMEs produce 558 tons of thrust at an isp of 452 seconds in a vacuum. That gives us a TWR of about 1.1 at liftoff. Slow but whatever.

A 10 ton payload (about the size of a soyuz) would give the vehicle a total dry mass of 55 tons and wet of 498. And a Delta V of 9.75 km/s. ENOUGH TO GET TO ORBIT! The S-II SSTO can drop off the cargo in LEO then deorbit.

This started off as a thought experiment but it is surprisingly doable I guess. The shuttle SRB parachute system landed the 90 ton dry SRBs at 23 m/s. I think it can land a 45 ton stage at 10-11 m/s no problem. Even then, solid retrorockets could be used to slow the stage down a bit as it lands.

One problem is the heatshield. I assume the existing S-II engine mounts are used for the SSMEs, although 2 are plugged up (only 3 engines). How do you fire an engine through a heatshield? Maybe put holes in the heatshield where the engines are, and use regenerative cooling during entry to keep the engines from melting.